The present invention relates to a method for producing an electroluminescent element (may be referred to as an abbreviation of EL) in which a pattern is formed.
EL elements attract attention as spontaneously emitting flat panel display elements in which positive holes and electrons, which have been poured into from opposed electrodes, are combined in a luminous layer to generate energy, and the energy excites fluorescent material in luminous layer to emit light of a color corresponding to the fluorescent material. Among them, an organic thin film EL display using an organic material as a luminescent material has such a high luminous efficiency that high intensity luminescence can be realized even if applied voltage is a little less than 10 V, is possible to emit light with a simple element structure, and is expected to be applied to low-cost simple expression displays such as advertisements and the like in which specific patterns are emitted and displayed.
In the production of a display using such an EL element, patterning on an electrode layer and an organic EL layer is usually put into practice. Methods of EL element patterning include a vapor deposition method of a luminescent material via a shadow mask, a method of separately painting through inkjet, a method of destroying specific luminescent pigment through ultraviolet irradiation, a screen printing method, and others. However, these methods could not provide an EL element being possible to realize all of the high luminous efficiency, the high light takeout efficiency, the simplicity of the production process, and the formation of highly fine patterns.
The present invention has been achieved in order to solve the above-mentioned problems. It is a main object of this invention to provide a method for producing an EL element for realizing the high luminous efficiency, the high light takeout efficiency, the simplicity of the production process, and the formation of highly fine patterns.
In order to achieve the object mentioned above, the present invention provides a method for producing an EL element, wherein at least one organic EL layer constituting the EL element is patterned by the use of a photolithography method.
According to a method for producing an EL element in the present invention, because the EL element is obtained by patterning at least one organic EL layer within the EL element by the use of a photolithography method, when compared to the conventional vapor deposition patterning method, the EL element can be produced relatively easily and in low cost because no vacuum equipment with high precision alignment mechanism and others are needed. On the other hand, when compared to the patterning method by the use of an inkjet system, the production method of the present invention is preferable in the point of no need of carrying out preprocessing to constructions and substrates aiding patterning, and further the production method can be considered to be preferable to higher precision pattern forming because of the relationship to the discharge accuracy of an inkjet head. Thus, according to the EL element production method of the present invention, a highly fine EL element can be obtained relatively easily and in low cost.
In the above-mentioned invention, it is preferable that an organic EL layer made by patterning with the use of the above-mentioned photolithography method is a luminous layer. Because in an EL element, a luminous layer is an indispensable layer and can obtain a highly fine pattern that is needed in case of light emission.
Further, in the above-mentioned invention, it is preferable that the above-mentioned luminous layer is insoluble in a photoresist solvent, a photoresist developing solution, and a photoresist peeling liquid, and a photoresist is insoluble in a solvent that is used in forming the above-mentioned luminous layer. Although depending on the kinds of photolithography methods such as, for example, a method of using dry etching, a method of using a dry film and the like, in case where the general wet photolithography method is used, it is preferable to use a luminous layer and a photoresist that satisfy such requirements.
In addition, in the above-mentioned invention, it is preferable that the above-mentioned luminous layer is a luminous layer in which different types of luminous layers are formed by the use of the photolithography method in plural times. Because when the luminous layer is formed in different types of plural luminous layers, full coloring is possible, for example, by selecting red, green, blue and the like.
In this case, it is preferable that a solvent used for forming a luminous layer in the above-mentioned luminous layers, which are formed in two times and after, is a poor solvent to the previously formed luminous layer. Because a solvent for forming a luminous layer that is used in a luminous layer to be newly formed is a poor solvent to the previously formed luminous layer, so no mixed color will be caused when a luminous layer is further formed on the previously formed luminous layer.
In this case, it is preferable that the solubility of the previously formed luminous layer to the solvent used for forming luminous layers formed in two times and after is 0.1 g or less/g of solvent at 25xc2x0 C. under 1 atmospheric pressure. This is the reason that, if the solubility is in this degree, even when a new luminous layer is formed on the previously formed luminous layer, the previously formed layer will not be dissolved in a solvent to cause mixed color.
Furthermore, it is also preferable that the above-mentioned luminous layers to be formed in plural times are formed in the order of the short wavelength of light obtained from them.
Generally, when two kinds of a luminescent material emitting light of high energy short wavelength and a luminescent material emitting light of low energy long wavelength are mixed, the light emission from the luminescent material emitting light of long wavelength becomes to be main. In the present invention, since luminous layers are planned to be formed in the order of the short wavelength of light emitted from them, a luminescent material for a luminous layer to be formed later becomes to be a luminescent material emitting light of a long wavelength, and even if the luminescent material used for forming the previously formed luminous layer is mixed in a luminous layer to be formed later, the short wavelength luminescent material in the previously farmed luminous layer that mixed in will hardly emit light, resulting In extremely lowering the possibility of causing problems like mixed color and others.
Like this, in case where luminous layers are formed in plural times, it is preferable that the above-mentioned luminous layers are three types of luminous layers emitting red, green and blue light. Because in order to make light emit in full color, it is generally preferable to make light emit in the three primary colors of red, green and blue.
Moreover, in the present invention, the above-mentioned organic EL layer that is made by patterning with the use of a photolithography method may be a buffer layer. In the present invention, it is preferable to use a photolithography method as mentioned above when a luminous layer is patterned, however the use of a photolithography method is not limited to this, the buffer layer may be patterned with the use of a photolithography. In particular, in an EL element in which a luminous layer is comprised of an organic polymer, it is preferable to combine a buffer layer and a luminous layer from the aspect of luminous efficiency, and on this occasion, through both layers are patterned with the use of a photolithography method, a cheap and high quality EL element can be produced.
In this case, it is preferable that the above-mentioned buffer layer is insoluble in a photoresist solvent and a photoresist peeling liquid, and a photoresist is insoluble in a solvent used for forming the above-mentioned buffer layer. This is the reason that, similarly to the case of a luminous layer as mentioned above, though depending upon the kinds of photolithography methods, it is necessary to satisfy the above-mentioned requirements in a photolithography method in which all procedures are carried out in wet conditions.
And, further, it is preferable that after a buffer layer that is insoluble in a photoresist solvent, a photoresist peeling liquid and a solvent to be used for forming a luminous layer is patterned and formed with the use of a photoresist that is insoluble in a solvent used in forming the buffer layer, a luminous layer that is insoluble in a photoresist solvent, a photoresist developing solution, and a photoresist peeling liquid is patterned and formed with the use of a photoresist that is insoluble in a solvent to be used in forming the luminous layer. As mentioned above, in an EL element in which a luminous layer is comprised of an organic polymer, it is preferable to combine a buffer layer with a luminous layer. Because it is preferable that in this case, a buffer layer that satisfies the above-mentioned requirements is first formed by a photolithography method, then a luminous layer that satisfies the above-mentioned requirements, is formed.
In the present invention, the above-mentioned patterning by the use of a photolithography method may be a patterning that after a photoresist is patterned in such a way that the photoresist is applied on an organic EL layer to be patterned, exposed and developed, the organic EL layer in the part where the photoresist has been removed is removed with dry etching.
Because it becomes possible to form highly finer pattern by the use of a method with which an organic EL layer can be dry etched like this.
In this case, the above-mentioned dry etching is preferable to be reactive ion etching. It is because the organic EL layer can be effectively removed by the use of reactive ion etching.
Furthermore, it is preferable to use a simple substance of oxygen or a gas containing oxygen in the above-mentioned dry etching. Because the use of a simple substance of oxygen or a gas containing oxygen can effectively remove the organic EL layer without affecting on glass and ITO with oxidation reaction.
In addition, it is preferable to use atmospheric-pressure plasma in the above-mentioned dry etching. It is because the use of atmospheric-pressure plasma makes it possible to delete the vacuum process and to carry out patterning with high productivity.
Further, in the present invention, the above-mentioned patterning by the use of a photolithography method is preferable to be a patterning that after a photoresist is patterned in such a way that the photoresist is applied on an organic EL layer to be patterned, exposed and developed, the organic EL layer in the part where the photoresist has been removed is removed in an ultrasonic bath.
It is because the use of such a method makes it possible to carry out high precise patterning without problems including the narrowing of each pattern and the outflow of materials for the organic EL layer, in the patterning of the organic EL layer with the use of a photoresist.
The present invention provides an EL element having at least one patterned organic EL layer, and the EL element wherein that it does not have any of partition, a structure aiding patterning, and surface treatment aiding patterning.
The EL element of the present invention has an advantage of low cost because it does not have a partition and others like this.
Further, the present invention provides an EL element having at least one organic EL layer, and the above-mentioned EL element layer wherein it is a patterned luminous layer and the width of an area with uneven film thickness that is formed at the edge of the above-mentioned patterned luminous layer is 15 xcexcm or less.
In the EL element of the present invention, because the width of an area with uneven film thickness is 15 xcexcm or less, it is possible to make the distance between patterns to be small and to make a highly fine pattern. Here, xe2x80x9can area with uneven film thicknessxe2x80x9d indicates an area where the film thickness is decreased from that of a flat part, that is, an area where the film thickness is equal to or less than 90% of the average film thickness of the flat part.
Furthermore, the present invention provides an EL element having at least one organic EL layer, and the above-mentioned EL layer wherein it is plural luminous layers that can emit light with plural colors and the distance between adjacent luminous layers emitting different colors is 30 xcexcm or less. Since the distance between pixels can be made small like this, a higher quality image can be displayed.
In these, it is preferable to have at least a substrate, an electrode layer formed on the above-mentioned substrate in the form of a pattern, and an insulating layer that is formed so as to cover the edge part of the above-mentioned electrode layer and the non-luminous layer of the element. Because it is possible to prevent shorts in parts unnecessary for luminescence and to decrease defects due to short of elements and the like to make an element that has a long life and can obtain stable luminescence.
According to the present invention, since the EL element is obtained by patterning at least one organic EL layer within the EL element by the use of a photolithography method, when compared to the conventional vapor deposition patterning method, the EL element can be produced relatively easily and in low cost because no vacuum equipment with alignment mechanism and others are needed. On the other hand, when compared to the patterning method by the use of an inkjet system, the production method of the present invention is preferable in the point of no need of carrying out preprocessing and others to constructions and substrates aiding patterning, and further the method can be considered to be preferable in the formation of higher precision patterns because of the relationship to the discharge accuracy of an inkjet head. Thus, according to the EL element production method of the present invention, a highly fine EL element can be obtained relatively easily and in low cost.
Further, according to the present invention, an EL element and the production method thereof will be provided for realizing all of the following subjects; no mixing of impurities in the luminous layer, the high luminous efficiency and the high light takeout efficiency, the simplification of production processes, the mass production system, the pattern formation being possible to emit highly fine and uniform light, and decreasing in crosstalk.
To be more concrete, for example, it is possible to decrease crosstalk in the drive of a simple matrix element by patterning a buffer layer. And, through patterning a buffer and luminous layers that are made by application, it is possible to carry out laser removal and insoluble part removal usually carried out by pulling out at the same time, and thus it is possible to simplify the processes. Further, it is also possible to simplify the processes from the viewpoint of the following fact; there is no need to use any of a partition, a structure having ink-repellent property to aid patterning and surface treatment having ink-repellent property to aid patterning. Moreover, the present invention is excellent in the points of being able to control and pattern the color of emitted light in any of an EL element emitting light in an optional pattern and an EL element emitting full color light, and further in an EL element using a flexible substrate.